Preparation of soluble nitrocellulose having carboxyl groups in the primary position



Patented Mar. 13, 1951 UNITED STATES OFFICE.

PREPARATION OF SOLUBLE NITROCELLU- LOSE HAVING CARBOXYL GROUPS IN THEPRIMARY POSITION No Drawing. Application April 10, 1948,

Serial No. 20,854

Claims. 1 This invention relates to acetone-soluble cellulose nitrateshaving carboXyl groups in the primary position and their preparation.

One object of my invention is to provide a cellulosic material havingboth a nitrate content and a carboxyl content which material is solublein acetone. Another object of m invention is to provide a process ofpreparing an acetonesoluble cellulose nitrate having carboxyl groups inthe primary position. A further object of my invention is to provide acellulosic material which will adhere to the surfaces of both cellulosenitrate and of organic acid esters of cellulose and is also reactivewith basic materials. Other objects of my invention will appear herem.

I have found that cellulose oxidized With N02 (or its dimer, N204) asdescribed in Yackel and Kenyon Patent 2,232,990 or in Kenyon and YackelPatent No. 2,448,892, when nitrated and then steeped in dilute aqueousalkali, gives. cellulosic material which is acetone soluble, is adherentto either cellulose nitrate or organic acid esters of cellulose whenapplied thereto from solution in a volatile solvent or when its estersare applied to the cellulosic material, and is susceptible to basicmaterials.

The cellulosic material of my invention is prepared by first oxidizingcellulose with N02 or N204 so as to impart a carboxyl content of 0.05%to approximately 6% thereto. The degree of oxidation of the cellulose isprimarily dependent upon the time of treatment. A time of 1-4 hours oftreatment with N02 is usually sufficient to give the desired carboxylcontent to the cellulose although the carboxyl content achieved maydepend to some extent on the rate of application of the N02 to thecellulose. If the cellulose is oxidized by treating it with a solutionof N02 in a solvent such as carbon tetrachloride, the concentration ofN02 as well as the time is important in determining the carboxyl contentattained. For instance, Examples 8 and 9 of Patent No. 2,448,892 showthe preparation of oxidized cellulose having a carboxyl content of 0.05%to 6% by means of a low concentration of N02 in carbon tetrachlorideeven though a long time of treatment is employed. This first step of myprocess is employed in such a manner that only a small carboxyl contentis imparted to the cellulose.

The cellulose oxidized as described is then nitrated to obtain a producthaving a nitrogen content of 10.5-12.2% of nitrogen. The nitrating bathused consists of 80-98% of nitric and sul- 2 furic acids, the remainderbeing made up principally of water. The HNO3H2SO4 in the nitrating bathshould approximate equal parts (that is, each being 40-60% of theirtotal); The nitration of the oxidized cellulose is carried out tosubstantial equilibrium with the particular nitrating mixture employed.Ordinarily a time of hour at room temperature is sufficient to obtaincomplete reaction although longer times of treatment may be employedalthough serving no useful purposes beyond 30-45 minutes. After thecellulose has been nitrated it is stabilized by subjecting to treatmentwith hot water although in some cases this hot water treatment may beunture or at room temperature. The time and concentration of alkalitreatment varies depending upon the alkali used. Ordinarily a time of 15minutes is desirable even under the best conditions although there havebeen exceptional cases where a time of as little as 5 minutes oftreatment of the cellulosic material with alkali solution has impartedacetone solubility. If sodium hydroxide is employed, a concentrationwithin the range of .01 to 0.4% should be employed and a temperature ofC. may be used. If desired, however, room temperature may be employedwith good effect. If barium hydroxide is used, it is desirable to employa concentration within the range of 0.1% to 31% and a temperature of 40C. to obtain acetone solubility although here again room temperaturewill be set. With calcium hydroxide it is desirable to employ asaturated solution thereof although a concentration may fall to as lowas 0.1% and still be effective in imparting acetone solubility. Withcalcium acetate the concentration may be from 0.1% to 10% to impartacetone solubility to the cellulose material being treated. In all ofthe al- 3 material being treated. The time of steeping, however, is notcritical and may be several hours such as up to hours. Other alkalies,such as sodium carbonate, sodium borate, or the like, may be employed,if desired, for treating the nitrate of oxidized cellulose to impartacetone solubility thereto. The criterion of this reagent is that it bea mild alkali or, if a pronounced alkali, that it be employed in adilute condition. The alkali used should not be so strong thatdegradation of the cellulose occurs which would be evidenced bydiscoloration of the product and decrease of its nitrogen content. Afterthe product has been treated with alkali to impart acetone solubilitythereto, it is desirable to wash with acid and then with water to removeall trace of. alkali therefrom. A product is thereby obtained which canbe dissolved up into acetone and used for coating, such as subbinglayers or anti-halation layers for photographic film, situations wheresusceptibility to dyeing with basic dyes are desired-or for adhesivepurposes oi various types.

The following examples illustrate my invention:

Example 1. parts of dried refined cotton linters having a cuprammoniumviscosity of 135- 200 centipoises was immersed for 2 hours in a mixtureof 80 parts of liquid N204 and 320 parts of carbon tetrachloride. Thematerial was then separated from the liquid and washed with 13 changesof distilled water until free of the N2O4CC14 mixture. The material wasdried and was found to contain 3.8% of carboxyl and 33% nitrogen. Theoxidized cellulose was then placed in a nitration mixture consisting of47.2% nitric acid,' l7.2% sulfuric acid, the balance being water, andthe treatment was maintained for 37 minutes at room temperature (70 F.).The product obtained was washed thoroughly with distilled water untilfree Of acid and then treated with a saturated aqueous solution ofcalcium hydroxide at 70 F. for 2 hours. This was .followed by treatmentwith 0.5 N HCl for one hour at 70 F. and then by hot (200? F.) distilledwater washes until a product was obtained which was free of acid andstable as shown by the German heat test. Theproduct obtained wascompletely soluble in acetoneand contained 12.16% nitrogen and 2.5%carboxyl.

Emample 2.20 parts of oxidized cellulose prepared as in-the precedingexample was nitrated with a mixture of 41.2% nitric acid, 41.2% su1-furic acid, and the balance water, for 37 minutes at 70 F. The productwas washed with distilled water until free of acid and portions thereofwere treated by each of three different alkalinemedia as follows:

A. A portion of the oxidized cellulose nitrate was treated'for 2 hoursat 70 F. with a 0.5 molar calcium acetate solution. The product was thencentrifuged free of excess liquid and immersed in 0.5 N HCl solution forminutes, then washed with hot distilled water until free of acid and wasfound to possess astability of at least 25 minutes as determined by theGermanheat test. The material was dried and was found to be completelyacetone soluble and to contain 11.64=% nitrogen and 1.08% carboxyl.

B. A portion of the distilled water-washed nitrated material was treatedfor 2 hours at 70 F. with a 0.1 molar barium hydroxide solution,followed by treatment with HCl and'hot distilled water as in A. Thesample obtained was completely acetone soluble and was found to contain11.48% nitrogen and 1.08% carboxyl.

C. In this case a saturated solution of calcium hydroxide was employedas the alkaline medium. A product was obtained completely soluble inacetone and containing 11.55% nitrogen and 1.08% carboxyl.

Example 3.--2 parts of dried refined cotton linters were immersed for 2hours in a mixture of 1 part N204 and 4 parts of carbon tetrachlorideusing a ratio by weight of 1 part of linters to 20 parts of N204mixture. The product obtained was washed thoroughly with distilled wateruntil free of the N2O4-CC14 mixture and was then dried. The carboxylcontent of the material was 1.9%. This oxidized cellulose was nitratedat 70 F. for approximately 30 minutes with a nitration bathconsisting of41.25% nitric acid, 41.25% sulfuric acid, and the balance water. tratedsample was washed with 0.1 N sodium hydroxide for /2 hour at 70 F. andthen with 0.5 N I-lClfor 10 minutes, followed by washings with hotdistilled water until stable as determined by a German heattest ofat'least'25 minutes. The nitrogen content of the final product was11.44% and the carboxyl content was 1.4%. This material was dehydratedwithn-butyl alcohol and made into a solution having a solids content of11% using as the solvent a mixture of 9 parts of methyl alcohol and 1part of acetone. A readily flowable solution was obtained suitable foruse for coatingpaper, fabrics, cellulose ester sheeting, or the like.The material in solution in volatile solvent could also be employed forthe preparation of cellulose ester products from which the volatileliquor could be readily evaporated.

The material prepared in accordance with my invention issusceptible toth action of basic dyes and any color desired may .be imparted theretowhether. after the material has been coated out in the form of a layeror prior to that coating operation. Also, this material may be reactedwith bases in order to incorporate ions therein by combining. with thecarboxyl. For instance, for some purposes it might be desirable to formthe copper,-zinc, or other metallio'saltoi this material. Ifdesired,amines may be reacted thereto to incorporate thatsubstituentchemically into the material. Due to this-property ofchemically combining with' cations it is desirable in the final washthereof that'only mineral-free water beemployed, as the carboxyl groupsof the material which I prepare mightotherwise combine with the cationsdu to the hardness inthe water.

I claim:

1. A method of preparing an acetone-soluble cellulose derivativewhich-comprises nitratingan oxidized cellulose having a carboxyl contentof .05 %-6% on thezprimary groups of the cellulose with a nitrating bathessentially consisting of a mixture ofHNOaand H2804, of -98% strength,each aoidconstituting 40+60% of the total acid present, so as to'imparta nitrogen content of l0.5.-12'.2% thereto an acetone-insoluble andalkali-insoluble product resulting and subsequently treating theso-prepared product with a mild alkali solution whereby substantiallycomplete acetone solubility is imparted thereto.

2. A method of preparing an acetone-soluble cellulose derivative whichcomprises nitrating an Noe-oxidized cellulose with a nitrating mixtureessentially consisting of a mixture of HNOs and H2804, of 80-98%strength, each acid constituting 40-60% of the total acid present, so asto impart a nitrogen content of 10.5-12.2% thereto an ace- Thenitone-insoluble and alkali-insoluble product resulting and subsequentlytreating the resulting product with a mild alkali solution wherebysubstantially complete acetone solubility is imparted thereto.

3. A method of preparing an acetone-soluble cellulose derivative whichcomprises nitrating cellulose having a carboxyl content of .05% to 6% onthe primary groups of the cellulose with a nitrating bath essentiallyconsisting of a mixture of HNOs and HZSO4, of 8098% strength, each acidconstituting 40-60% of the total acid present, so as to impart anitrogen content of 10.5-12.2% thereto an acetone-insoluble andalkali-insoluble product resulting and subsequently soaking the productso obtained in dilute aqueous sodium hydroxide having a concentration of.01-0.4% until a substantially completely acetone-soluble prod.- uct isobtained.

4. A method of preparing an acetone-soluble cellulose derivative whichcomprises nitrating cellulose having 05% to 6% of carboxyl on theprimary groups thereof with a nitrating bath essentially consisting of amixture of HNO3 and H2804, of 80-98% strength, each acid constituting40-60% of the total acid present, so as to impart a nitrogen content of10.5-12.2% thereto an acetone-insoluble and alkali-insoluble productresulting and subsequently treating the so-prepared product with anaqueous solution of calcium acetate having a concentration of .1 to 10%Whereby substantially complete acetone solubility is imparted thereto.

, droxide having a concentration from 0.1% up to a saturated solutionthereof for a sufficient time to impart substantially complete acetonesolubility to the resulting product.

WILLIAM E. SILLICK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,256,391 Hiatt Sept. 16, 19412,472,591 Kenyon et al June 7, 1949 OTHER REFERENCES Berl et al.: ZurichPolytech Z. ges. Schiess- Sprengstofie, vol. 2, pp. 381-387 (1907).

Davidson: J. Textile Inst., vol. 29, pp. T to T218 (1938).

3. A METHOD OF PREPARING AN ACETONE-SOLUBLE CELLULOSE DERIVATIVE WHICHCOMPRISES NITRATING CELLULOSE HAVING A CARBOXYL CONTENT OF .05% TO 6% ONTHE PRIMARY GROUPS OF THE CELLULOSE WITH A NITRATING BATH ESSENTIALLYCONSISTING OF A MIXTURE OF HNO3 AND H2SO4, OF 80-98% STRENGTH, EACH ACIDCONSTITUTING 40-60% OF THE TOTAL ACID PRESENT, SO AS TO IMPART ANITROGEN CONTENT OF 10.5-12.2% THERETO AN ACETONE-INSOLUBLE ANDALKALI-INSOLUBLE PRODUCT RESULTING AND SUBSEQUENTLY SOAKING THE PRODUCTSO OBTAINED IN DILUTE AQUEOUS SODIUM HYDROXIDE HAVING A CONCENTRATION OF.01-0.4% UNTIL A SUBSTANTIALLY COMPLETELY ACETONE-SOLUBLE PRODUCT ISOBTAINED.